Error notice generated

Hi, Upon activating WP_DEBUG; the Events Calendar plugin generates an error notice, as per below. Somehow it’s in conflict with another Plugin.
It apparently creates a session without protecting against the possibility that a session could have already been started elsewhere.
Here’s one of the notices:
Notice: Undefined property: WP_Query::$tribe_is_event_query in /customers/a/5/6/mooisteenwijkerland.nl/httpd.www/wp-content/plugins/the-events-calendar/lib/the-events-calendar.class.php on line 2117 Warning: session_start(): Cannot send session cache limiter – headers already sent (output started at /customers/a/5/6/mooisteenwijkerland.nl/httpd.www/wp-content/plugins/the-events-calendar/lib/the-events-calendar.class.php:2117) in /customers/a/5/6/mooisteenwijkerland.nl/httpd.www/wp-content/plugins/business-directory-plugin/wpbusdirman.php on line 360

https://www.ads-software.com/extend/plugins/the-events-calendar/